SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    26863, 43796, 4237, 43798, 5270, 5257, 
    6070, 37849, 335, 5726, 5288, 40809, 
    5228, 18194, 5265, 40754, 4279, 40807, 
    926, 1266, 26851, 32360, 1542, 6103, 
    26857, 37942, 2449, 31904, 31618, 6102, 
    31646, 35735
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00699

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "11",
          "used_key_parts": ["product_id", "lang_code"],
          "rows": 32,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (26863,43796,4237,43798,5270,5257,6070,37849,335,5726,5288,40809,5228,18194,5265,40754,4279,40807,926,1266,26851,32360,1542,6103,26857,37942,2449,31904,31618,6102,31646,35735) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}